Infectious bronchitis virus (IBV) is a group 3 avian coronavirus that causes a highly contagious upper-respiratory tract disease in chickens characterized by tracheal rales, coughing, and sneezing. In addition, the disease may affect the kidneys, and in laying flocks there is usually a drop in egg production and egg quality. Mortality may occur in young chicks due to respiratory or kidney manifestations of the infection. The disease is prevalent worldwide with significant economic consequences.
Control of the disease is extremely important because IBV predisposes birds to potentially lethal secondary pathogens. Attenuated live vaccines and killed vaccines are used in an attempt to prevent the disease. However, extensive genetic diversity and a high mutation rate results in many different types of the virus that do not serologically cross-react, making it important to vaccinate chickens with the type of IBV causing the disease. IBV variant viruses are consistently circulating in commercial poultry and are capable of causing disease outbreaks. There is little cross-protection between different serotypes of IBV.
Control of IBV relies primarily on the use of mass applied modified live vaccines. Poultry producers face several challenges when trying to control IBV infections in the field. First, very little to no cross-protection is afforded between serotypes of IBV. Therefore, successful vaccination programs must include the serotypes of the prevailing IBV field challenge. Second, IBVs are prone to genetic variation through several distinct genetic mechanisms that may or may not give rise to a new serotype. A few changes in the sequence of the spike glycoprotein can result in a new serotype. It has been documented that as little as a 5% difference in the S1 sequence of IBV can result in a loss of cross-protection between otherwise similar isolates (Cavanagh, 2003, Avian Pathol; 32:567-582).
Identifying the type of IBV causing disease in commercial chickens is the first step in controlling this highly infectious virus, but it is of little value if commercially available vaccines do not protect against it. Thus there is a need for the characterization of newly arising IBV variant and the development of vaccines effective against these variants.